In general, a ceramic filter exhibits excellent thermal resistance and corrosion resistance and has been used for, for example, efficiently collecting particulate matter (hereinbelow, referred to as “PM”) having a wide particle size distribution, such as soot exhausted from a diesel engine.
However, a relationship between PM collection efficiency and pressure loss tends to be incompatible. For example, when a pore size is too large, PM passes through the filter without being trapped, leading to low collection efficiency. When the pore size is too small, the pressure loss becomes large due to resistance to the passing gas, leading to an increase in a load on the engine, and further to clogging of the small pores, and as a result, increase in the pressure loss becomes drastic and a long-term use becomes difficult.
Therefore, there has been a conventional ceramic filter made of silicon carbide in which the collection efficiency and the pressure loss are adjusted (see, for example, Patent Document 1).
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